The BIA scan: A valuable measure of body composition?

Sep 25, 2019

I can’t be the only one that’s noticed Bioelectrical Impedance Analysis (BIA) scans popping up in just about every gym 12-week challenge, or ‘get fit for summer’ promo. These scans are advertised as a ‘new’ and ‘improved’ way to accurately measure your body composition that’s not going to cost you an arm and a leg. But should you be relying on this measure when it comes to achieving your goals?

It’s a BIG NO from us. Let me tell you why…

How BIA works:

This method of body composition measurement relies on different types of tissue in our bodies having different levels of conductivity. The machine sends a small current between the body parts in contact with the machine (either two or four points) and creates a measure of body composition depending on the response to this current. This is where we start to run into issues...

BIA machines with only two contact points (i.e. hand-to-hand, or foot-to-foot) only send a signal between this loop. They don't measure your entire body. Electrical currents will always take the path of least resistance from one point to another. So a stand on BIA with only two contact points at the feet measures the lower loop of your body. Up one leg and down the other. It typically misses scanning your entire upper body from belly up.

A hand to hand contact machine again measures this loop and skips your entire lower body making them completely inaccurate. For an individual who holds more fat through their hips and legs, this type of scan will completely underestimate body fat percentage. And on repeat measures, will underestimate fat loss as you can’t show a loss of mass that was never measured in the first place.

A BIA machine that measures using four-points e.g. you stand on contact points and hold onto them as well, is going to scan the whole body but is still not ideal. Read on...

So how is body composition measured?

Lean body tissue (bone and muscle), has a higher water and electrolyte content compared to fat mass. This means lean tissue has a greater conductivity, allowing the electrical current to pass through it easier. The lower the reading of electrical impedance, the higher the lean body mass of the individual.

The issue is that the water content of tissues can change depending on your hydration status. Hydration status is altered by water lost and gained throughout the day. When you eat carbohydrates, they’re broken down to the simplest form of glucose which, if not immediately used, is stored in your muscles as glycogen. The kicker is, water is stored with this glycogen too, increasing water content and making the muscle better at conducting electricity.

So essentially the less glycogen you have stored, the MORE resistance a muscle will place on the electrical current (2), and the higher the electrical impedance reading will be. We would incorrectly interpret this lower electrical resistance reading as higher lean body mass. In other words, any condition that depletes your muscle glycogen stores or dehydrates you will trick the machine into reading a higher fat mass (2). This means BIA can be inaccurate after a heavy training session, a big night out or on a low carbohydrate or a ketogenic diet to name a few scenarios.

So depending on your training and dietary habits in the days leading up to the test, results can vary significantly – in fact, a variance of up to 8% has been seen (6). To put this into perspective, a scan on an individual who had reduced their body fat percentage by 4% could actually read an increase of 4% body fat. Not exactly a reliable measure.

When we looked at the research available on the validity of BIA measures we discovered a whole host of different results for different populations: athletic and non-athletic. Some studies saw similar results to that of a DEXA (the gold standard in body composition measurement), while others over-estimated lean mass and underestimated fast mass and vice versa (1,2,6). All in all, this demonstrates a significant lack of accuracy, one we're far from comfortable with.

How is the estimation made?

BIA equipment uses a prediction equation developed from a different method of body composition analysis (e.g. hydrostatic weighing/DEXA), estimating your body composition based on the averages of a tested population. This prediction can become an issue for two reasons: 1) if there were inaccuracies in the original body composition measure and 2) if the population originally tested doesn’t have a similar body composition to you. We could be comparing a new gym member just getting started to a high performing athlete…

So what are the implications of this inaccuracy?

Although it may seem quite harmless when used in a gym setting (for those looking to lose a little fat or gain a little muscle), striving to improve through an inaccurate measure is detrimental to your progress. You’re setting yourself a moving target. You’re setting goals that will change depending on your hydration status and the extent the results have varied within that 8%. The reality is, there is absolutely no point in measuring something if it cannot accurately track progress. What you are doing is simply getting a number for the fun of it, a number that may or may not reflect your actual body composition at the time.

What to do instead:

Our advice is instead of throwing your money into an inaccurate measure, choose a DEXA or skinfold measurement (or both!) instead. If you're looking for an affordable, repeatable measure that isn’t impacted by hydration status then skinfolds are your best option here.

There are also several other measures that you can use from home that cost nothing!

Progress photos

Clothing size

Girth measurements

Weight (although be cautious with this one depending on your goal)

If you’re interested in tracking changes in your body composition accurately, book in for skinfold measurements with a qualified ISAK Anthropometrist today (not just some random PT wielding callipers). They can also guide you on an accurate DEXA scanning location (as there are errors associated with this method too!)

But remember, getting a measurement is only one small step towards goal progression. If you’re working towards a body composition goal, book an appointment with a Sports Dietitian to help you maximise your results.